This invention relates to a flexible, solid intumescent composition which acts as a seal in deterring the spread of fire, smoke, and fumes, and is especially adaptable as fire resistant glazing strips for metal and wood window frames, doors, dampers and shutters, and may also provide sealing where items such as plastic pipes and electrical cables pass through openings.
Fire, smoke, and fumes in confined spaces, such as multi-floor buildings, can be extremely life threatening. Frequently, if fire originates in the space between a floor and ceiling of such a structure, the fire, and resultant smoke and fumes, will tend to spread to other open spaces in the building, especially to open spaces above the point of origin of the fire.
The openings in floors, walls, and ceilings and the conduits, piping, cables, and the like that pass through are known as xe2x80x9cthrough-penetrationsxe2x80x9d. If not protected by fire resistant materials, a through-penetration offers an area of low resistance to fire, smoke, and fumes, and in essence may serve as a chimney for heat, flame, smoke, and fumes. The spaces between these conduits, piping, etc. may be filled and blocked with commercially available fire retardant and intumescent putties, caulks, wraps, sheets or mats, known in the art as xe2x80x9cfirestops.xe2x80x9d
Representative firestop products are disclosed in product brochure number 98-0400-4875-7 (published 1997) from Minnesota Mining and Manufacturing Company (3M). The 3M products are currently known under the trade designations xe2x80x9c3M Brand Fire Barrier CP-25WB+xe2x80x9d and xe2x80x9cInteram(trademark) Firedam 150xe2x80x9d (caulks); xe2x80x9c3M Brand Fire Barrier MPP-1+, MPP-4S+, MPP-5S+, and xe2x80x9cMPS-2+xe2x80x9d (moldable putties); xe2x80x9cFS-195+ A/P Stripxe2x80x9d (wrap/strip), xe2x80x9cFS-195+ AP+, AA+ and RR+xe2x80x9d (sheets); and CS-195+ (metal reinforced sheet). These products are described in U.S. Pat. Nos. 5,175,197; 5,059,637; 5,476,891; and 5,578,671. Other intumescent materials have been used, such as those known under the trade designations xe2x80x9cPalusolxe2x80x9d (commercially available from BASF) and xe2x80x9cExpantrol(trademark)xe2x80x9d (commercially available from 3M), the latter being a hydrated alkali metal silicate.
Intumescent sealing strips or other profiles are often required to prevent the spread of fire in buildings and other enclosed spaces. Intumescent materials expand when heated to fill up any spaces left by combustible materials which are consumed by the fire. In the case of glazing seals, these profiles also help to keep glass panels in place during a fire.
Such materials should also form a strong char when heated. The char formed should be resistant to erosion by exposure to the heat and pressures encountered during a fire. It is advantageous to minimize the amounts of smoke and toxic gases generated by such sealants during a fire.
These sealant materials should have good aging properties and resistance to environmental agents normally encountered. Ideally they should last at least as long as the building in which they are installed.
There continues to exist a need in the art for improved fire sealing compositions that are flexible, can be extruded into a variety of shapes, and have the capability of expanding many times their original volume when exposed to heat.
The present invention provides for the preparation, at a moderate cost, of a fire sealing composition which is flexible, solid and capable of being applied in various shapes including sheets, extruded strips or other profiles. The composition exhibits an excellent combination of fire resistance, flexibility, char strength, and water resistance.
It has been discovered that compounding ingredients under high shear conditions in a substantially volatile-free condition results in fire barrier materials with improved tensile properties, improved Shore and penetrometer hardness values, and higher volumetric expansions upon exposure to fire or extreme heat when compared to formulations which were prepared with a volatile solvent or carrier present. For example, fire barrier materials obtained by high shear compounding with polymer from a dried latex demonstrated significantly improved properties over control formulations with the same ingredients which were thoroughly mixed in the wet state and then allowed to dry without high shear mixing in the dry state. It is difficult to obtain sufficiently high shear during compounding when a volatile solvent or carrier is present. Mixing of ingredients which would result in a composition having a value in a penetration test, as described below, greater than about 4 mm may not introduce sufficiently high shear even in a substantially volatile-free state. The required high shear mixing conditions are typically met when a resulting fire barrier material has a penetration test value less than about 4 mm and when thorough mixing of the fire barrier material ingredients is performed in a state which is substantially free of volatiles.
Accordingly, the present invention includes a flexible, solid fire sealing composition comprising: (a) water-insoluble intumescent mineral granules; (b) a thermoplastic or thermosetting, halogen-free binder; and (c) a phosphorus containing flame retardant, wherein said composition has a softness value from about 0.01 to about 3.75 mm.
A second aspect of the present invention is a process for preparing a flexible, solid fire sealing composition including the step of high shear mixing in a substantially volatile-free state: (a) water-insoluble intumescent mineral granules, (b) a halogen-free organic binder, and (c) a phosphorus containing flame retardant, wherein the resulting composition has a softness value (penetrometer) of from about 0.01 to about 3.75 mm.
The intumescent material is made of water-insoluble mineral granules, such as for example hydrated alkali metal silicates, preferably such silicates incorporating an oxy boron compound, e.g. 3M Expantrol(trademark) 4BW.
The organic binder is a thermoplastic or thermosetting, halogen-free polymeric material. The thermoplastic or thermoset organic polymers used as the binders also provide the flexibility required, good char strength and a high level of intumescence in combination with the intumescent granules.
The use of halogen-free binder materials eliminates the risk of formation of toxic and corrosive halogen acid gases during a fire. The use of halogen-free binder materials requires the addition of a flame retardant to the composition of the present invention.
The fire sealing compositions of the present invention are an advance over the art because of their improved tensile strength, Shore hardness and lower penetrometer value. When subjected to heat, they also exhibit higher volume expansion values that are beneficial in sealing penetrations during a fire. Another distinguishing feature of the present invention is the fact that the compositions are not only flexible but solid, i.e. substantially free of volatiles, e.g. water or organic solvents. A small quantity of liquid plasticizer may optionally be incorporated, but the overall composition is solid at room temperature and does not exhibit the flow properties of a water- or solvent-borne dispersion of a caulk, mastic, paint or coating material.
The compositions of the present invention are also distinguishable from putty-like materials which are soft and malleable at room temperature. As noted above, the compositions of the present invention, although flexible, have a well-defined shape to which they will tend to revert following small deformation.
Other aspects of the present invention are methods of fire stopping a through-penetration, door or window, the methods including the steps of applying the composition of the invention above described to a through-penetration, door or window and allowing the composition to expand and char upon exposure to heat.
The process of the present invention requires high shear mixing of the components in a volatile-free state. The resulting fire sealing compositions are flexible and intumescent (expand when heated). Preferably the seals are thermoplastic or elastomeric and may be prepared using standard molding or extrusion techniques for high shear mixing and shaping thermoplastic polymers or elastomeric rubber-like materials. The compositions or materials may either be cured (thermosetting) or uncured (thermoplastic). In general, uncured materials give rise to higher expansion levels, whereas cured materials have improved elastic properties and may also have higher char strength.
The compositions of the present invention incorporate at least three ingredients, namely an intumescent material, a halogen-free organic binder, and a flame retardant.
The intumescent materials are water-insoluble mineral granules. Intumescent material may be a granular hydrated alkali metal silicate such as described in U.S. Pat. No. 4,273,879 (Langer et al.), incorporated herein by reference. The preferred alkali metal silicates described in the ""879 patent are granulated sodium silicates having a moisture content of about 5 to about 30 weight percent, a silicon dioxide (SiO2) to sodium oxide (Na2O) ratio ranging from about 2.0:1 to about 3.75:1, and particle sizes ranging from about 0.2 mm to 2.0 mm (i.e. about 95% of the particles being greater than 0.2 mm).
A preferred water-insoluble mineral granule is a mixture of alkali metal silicate represented by the formula M2O:xSiO2 in which M is an alkali metal. The mixture also includes at least one oxy boron compound which may be selected from boric acid and borate salts of Group I and II elements and water. The weight ratio X ranges from about 1.5 to about 4, the molar ratio of boron to M is between about 0.2 and about 0.9, and the water comprises about 5 to 15 weight percent of the total composition.
There are many silicates which could be used. Examples cited in Graham et al., U.S. Pat. No. 4,521,333 include sodium silicate, lithium silicate and potassium silicate.
There are many oxy boron compounds which could be used for the present invention. Examples cited in Graham et al. ""333 of oxy boron compounds include metaborate, tetraborate, perborate, polyborate radicals, boric acid, colemanite, calcium metaborate, magnesium borate and zinc borate.
Other intumescent compounds may be used especially if admixed with the above silicates. These intumescent compounds include, for example, expandable graphite, vermiculite, perlite, NaBSi, glass particles, mica, inorganic and organic blowing agents and mixtures thereof. Preferred intumescent graphite materials include: Kropfmuehl A15/90 commercially available from Graphitwerk Kropfmuehl A G, Hauzenberg, Germany; Sigraflex FR 90-60/80 Type 2, commercially available from Normann Rassmann GMBH and Co., Hamburg, Germany; and Expan-C-8099 LTE commercially available from Lineta, Kobenhavn, Denmark. Such graphite may be admixed with the granulated hydrated alkali metal silicate intumescent composition mentioned above under the trade designation xe2x80x9cExpantrol(trademark) 4BWxe2x80x9d from 3M Company of St. Paul, Minn. The amount of intumescent material typically may range from about 10 to about 70 wt- %, preferably from about 25 to about 60 wt- %, based on a total weight of fire sealing composition.
The second component is a halogen-free organic binder. This material is a thermoplastic or thermosetting binder.
xe2x80x9cThermoplasticxe2x80x9d materials typically have long polymer chains with few, if any, chemical bonds acting to crosslink the chains. Thermoplastic materials, when heated, normally become soft and moldable to a desired shape. Subsequent reheating serves to resoften the material. Examples of thermoplastic materials include substantially linear polymers such as acrylate polymers, ethylene vinyl acetate copolymers, natural rubbers, styrene butadiene copolymers, butadiene acrylonitrile copolymers, polyisoprene, polybutadiene, polyvinyl acetate, polyethylene terephthalate, polyethylene, polypropylene, polystyrene, and combinations and mixtures of these polymers. The term xe2x80x9csubstantially linearxe2x80x9d as used with reference to these materials refers to a preference for no more than three or four branches on average per polymer chain, preferably one or two, and most preferably zero.
xe2x80x9cThermosetxe2x80x9d materials refer to polymers which undergo crosslinking reactions and thus cure or xe2x80x9csetxe2x80x9d, typically upon heating. If the crosslinking density is sufficiently high, the material tends to be hard, infusible, and insoluble. The shape of such materials typically cannot be subsequently permanently changed if warmed. Two or more liquid components can be reacted to form a thermoset polymer; for example, a multifunctional amine and a multifunctional epoxy may be reacted to form an epoxy system. Examples of suitable thermoset materials include epoxies, phenolics, polyesters, silicones, polyurethanes, polyimides and the like. In addition, suitable thermoset materials include thermoplastic materials capable of being crosslinked with the addition of a crosslinking agent and/or exposure to an appropriate energy source such as an electron beam. The materials include, for example, natural rubber, styrene butadiene copolymers, butadiene acrylonitrile copolymers, and polybutadiene.
If the binder is in the form of a latex, the latex material must be dried prior to the high shear mixing to remove water and other volatiles, if present.
Preferred thermoplastic or thermosetting binders include synthetic or natural isoprene rubber, ethylene propylene rubber, EPDM rubber, and polybutadiene. The most preferred binder contains an ethylene vinyl acetate copolymer. Blends of these materials, e.g., ethylene vinyl acetate/synthetic isoprene rubber may also be employed.
The amount of binder may typically range from about 10 to about 50 wt- %, preferably from about 12 to about 40 wt- %, based on the total weight of the fire barrier material.
A third ingredient in the fire sealing composition is a flame retardant. This flame retardant is preferably a phosphorous and/or nitrogen containing material which promotes the charring of organic binders by forming an acid when heated. Preferred phosphorous containing compounds include compounds containing ammonium polyphosphate (APP). Thus, examples of such phosphorus containing products include Exolit IFR-10, Spinflam MF82/PP (both of which contain APP), and Amgard EDAP (ethylenediamine phosphate) and NH1197 (believed to be a phosphate salt of pentaerythritol). Endothermic materials are also appropriate flame retardants. A preferred endothermic material is, for example, alumina trihydrate.
Typically flame retardant compounds, when present, are in an amount ranging from about 10 to about 50 wt- %, preferably about 15 to about 40 wt- %, based on the total weight of the fire sealing composition.
Further optional ingredients may also be present to add or enhance the properties of the fire sealing composition and may include fillers, pigments, and processing aids. In addition, since thermosetting materials may be employed as a binder, curative or crosslinking agents may be present such as, for example, organic peroxides such as dicumyl peroxide.
Plasticizers, preferably a flame retardant plasticizer, most preferably an organic phosphate plasticizer, e.g. SANTICIZER 141 or 148 from Monsanto, may also be used. The amount of plasticizer should be limited to avoid the composition becoming too soft or putty-like. A plasticizer may be used as a process aid in extruding or molding the sealant in its desired shape.
Antioxidants and anti-ozonants may also be used, e.g. hindered phenolics, aromatic amines and others, such as for example, Irganox 1010. Colorants such as organics, e.g. pigments, lakes or dyes, or inorganic pigments, e.g. titanium oxide, zinc oxide or iron oxides, may also be added as desired.
The process of the present invention is carried out by combining the ingredients used through a high shear mixing operation where such mixing is carried out in a volatile-free state. Typically, the composition is made by high shear mixing of the various ingredients using for example, a 2-roll mill, Banbury mixer, or, preferably, a twin-screw extruder equipped with heating/cooling capabilities to control the processing temperature.
The term xe2x80x9ca substantially volatile-free statexe2x80x9d means that the high shear mixing takes place in a chamber where the components of the composition are free of volatile organic solvents and the binder is also essentially free of water (i.e., containing less than 0.25% by weight). This water being other than bound water, wherein bound water is water that does not evaporate until the material is heated to at least 100xc2x0 C. (preferably, at least 150xc2x0 C., more preferably at least 250xc2x0 C.).
The binder is either pre-dried, e.g. in an oven, or, if dry, directly added to the mixing chamber and mixed until thoroughly blended. Any fillers, processing aids, char forming resins, waxes, colorants, flame retardants, antioxidants, antiozonants, curatives, and plasticizers are then added while the mixing operation continues. The last ingredient added is usually the intumescent material. The composition is typically mixed until homogeneous and smooth (i.e., not lumpy).
The composition can also be prepared by adding the ingredients to a heated zone of a twin screw extruder where volatiles, if present, are removed prior to entering a mixing zone. Following mixing, the composition is extruded into various shapes and sizes, e.g., profiles, sheets, and strips. The shape and size are dictated by the application.
The compositions of the present invention have utility as fire resistant glazing strips/profiles and as fire and smoke seals for fire rated doors, dampers, shutters, and penetration seals.
The following examples are provided to further illustrate the present invention and are not intended to be limiting thereon. The ingredients used for the examples are listed in Table 1, below.